Smoke divers usually work in extremely difficult conditions in environments where the temperature is very high due to fire and visibility is very poor due to smoke from a fire and where besides the noise level is high due to fire extinguishing operations. Scuba divers also sometimes work in difficult conditions with poor visibility. Smoke divers, but also scuba divers working in difficult conditions, therefore mostly work in pairs, and of course it is necessary for both individuals in each pair to have contact with each other while performing the work. This is particularly important for security reasons. If one of the divers should be injured or in some other way get into danger, it is necessary that the other diver's attention can be quickly drawn to this so that he can rescue his colleague.
The smoke divers are often provided with a communication radio system to be able to communicate with each other. However, this does not function if one of them has become unconscious or for some other reason is not capable of using his radio equipment. A prior art alarm device consists of a box which the smoke diver carries on his stomach and which emits an acoustic signal if the smoke diver is lying or for some other reason has not performed an activity for a period of time of about 20 s. The emitted acoustic signal is, however, not always a sufficient aid to quickly locating a diver in danger. A further prior art device for locating a smoke diver in danger is a unit, which is provided with flashing light emitting diodes and which the smoke diver also carries on his stomach. Such light emitting diodes have a short range in a space filled with smoke from a fire and, in addition, they are completely shielded if the smoke diver's back is directed towards the person looking for him, or if he is lying face down.
Thus, there is a great need for a device that functions well in the above described difficult environments and is adapted to locate in particular a smoke diver, but also a scuba diver.